diff --git a/src/micropolisj/engine/MapScanner.java b/src/micropolisj/engine/MapScanner.java
index f921271..e48d92c 100644
--- a/src/micropolisj/engine/MapScanner.java
+++ b/src/micropolisj/engine/MapScanner.java
@@ -275,6 +275,14 @@ class MapScanner
 
 	/**
 	 * Called when the current tile is a road bridge over water.
+	 * Handles the draw bridge. For the draw bridge to appear,
+	 * there must be a boat on the water, the boat must be
+	 * within a certain distance of the bridge, it must be where
+	 * the map generator placed 'channel' tiles (these are tiles
+	 * that look just like regular river tiles but have a different
+	 * numeric value), and you must be a little lucky.
+	 *
+	 * @return true if the draw bridge is open; false otherwise
 	 */
 	boolean doBridge()
 	{
diff --git a/src/micropolisj/engine/TileConstants.java b/src/micropolisj/engine/TileConstants.java
index 7da0da3..047580d 100644
--- a/src/micropolisj/engine/TileConstants.java
+++ b/src/micropolisj/engine/TileConstants.java
@@ -135,7 +135,7 @@ public class TileConstants
 	public static final char NUCLEAR = 816;
 	public static final char LASTZONE = 826;
 	public static final char LIGHTNINGBOLT = 827;
-	public static final char HBRDG0 = 828;
+	public static final char HBRDG0 = 828;   //draw bridge tiles (horz)
 	public static final char HBRDG1 = 829;
 	public static final char HBRDG2 = 830;
 	public static final char HBRDG3 = 831;
@@ -152,7 +152,7 @@ public class TileConstants
 	public static final char COALSMOKE4 = 928;
 	public static final char FOOTBALLGAME1 = 932;
 	public static final char FOOTBALLGAME2 = 940;
-	public static final char VBRDG0 = 948;
+	public static final char VBRDG0 = 948;   //draw bridge tiles (vert)
 	public static final char VBRDG1 = 949;
 	public static final char VBRDG2 = 950;
 	public static final char VBRDG3 = 951;